Couplings of this type are already known in regard to commercial vehicles. A large number of designs have been published for couplings in tractor trailer design.
Customarily, a saddle mounted trailer equipped with such a coupling is attached to a tractor unit by a centrally positioned kingpin penetrating a support disk. This arrangement is referred to as a “fifth wheel”. A saddle connection consists of a coupling plate having a recess, into which a kingpin can be inserted and be locked against turning by a closure mechanism. The surface of the coupling plate defines the plane of slewing between a tractor and a trailer at the coupling level. At the same time, this surface is made frictional and upon which a plate encompassing the kingpin can safely rotate. In this way, the tractor and the trailer are bound together and enabled to turn about the kingpin. In the case of certain conditions of driving, especially where brake action occurs in sharp turnings, jack-knifing can occur, wherein the tractor and the trailer reach a minimum angle of closure together, so that the entire vehicle assembly is no longer controllable. A swinging of the trailer back and forth in increasing arcs can occur under some circumstances. Like problems are found with articulated busses, truck trailers and even conjoined rail cars.
A generally accepted concept is based on a principle that a saddle linkage is to be stiffened by a more or less strongly damped brake arrangement, i.e. by a an appropriate damping apparatus. U.S. Pat. No. 3,231,295 proposes, for example, a rotatable kingpin arrangement in the trailer connection, which exhibits its braking effect by a brake drum and a loop-type brake. The braking action is carried out, in this case, with a rod, which engages the motor vehicle brake assembly. U.S. Pat. No. 4,065,149 proposes a rotating, saddle plate installed on a tractor about a vertical axle. This saddle plate is to be turn-fast attached to the trailer extension by an oval kingpin. The rotation of the saddle plate can be restricted by an internally placed, pneumatic drum brake. The operation of this arrangement can be initiated by the brake system of the vehicle. GB 2 365 398 discloses a damping system interposed between the tractor and the trailer, which is intended to repress a tendency to jackknife. To accomplish this purpose, a hydraulic damping element is provided, the resistance of which is adjustable by opening and closing a compensation system. The damping can be carried out by either visco-electric or visco-magnetic means.
The damping here can have a relation to the angle posed by the tractor and trailer to one another, which may be measured by the relation of the brake action of the vehicle. U.S. Pat. No. 5,690,347 brings forth another concept, wherein the brake assembly operates with brake elements, which act simultaneously between the tractor and the trailer and are designed as eccentrically operating brake cylinders. GB 1 205 314, US 2005/0212256 A1 and DE 29 49 933 all present further ideas.
The demands made on a functional coupling apparatus are contradictive: first, it is necessary to create an enormous braking moment in order to restrain a jackknife effect, when one considers the weight of loaded tractor trailer units, which units are commonly used in commercial service. Second, a compact and space saving construction is required, so as not to interfere with payable volume, i.e. load, to be carried. The above cited concepts only partially fulfill the requirements. None of them dominate practical applications. A further demand is that a coupling having a brake system or may be easily mountable must be integrated into existing, standardized dimensioning.